Method for liquid-developing an electrostatic image

ABSTRACT

An electrophotographic liquid-developing method comprising controlling the polarity of the toner by varying the mixing proportion of the dispersion media and/or the temperature of the developer solution. An electrostatic charge-substrate having an electrostatically charged latent image is immersed in the developer solution to convert such latent image into a visible image. Said developer solution comprises a toner consisting of pigment particles and at least one resin selected from the group consisting of alkyd resin, phenol resin and vinyl resin, and a carrier liquid in which said toner is dispersed. The carrier liquid comprises a mixture of two dispersion media having different affinities to said resin. Dispersion media having a larger affinity to the resin include halogenated hydrocarbons, aromatic hydrocarbons and petroleum hydrocarbons containing aromatic ingredients. Dispersion media having a smaller affinity to the resin include isoparaffinic and paraffinic hydrocarbons.

- 0 United States Patent 51 3,640,751 Kasuya et al. 1 Feb. 8, 1972 [54] METHOD FOR LIQUID-DEVELOPING 3,356,498 12/1967 Moe et a1 ..117/37 X AN ELECTROSTATIC IMAGE 3,357,828 12/1967 Moe ...1l7/37 X 3,438,004 4/1969 Wagner..... 117/37 X 21 Inventors: Kamhlko y Kawasaki-sin; u- 3,444,083 5/1969 Oliphan't... ..117/37 x ro Ohta; Zeniiro Okuno, both of Tokyo,

all of Japan Primary Examiner-William D. Martin Assistant Examiner-M. Sofocleous [73] Assignee. Kabushikr Kaisha R coh, Tokyo, Japan Anamey w Blanchard and Flynn [22] Filed: Oct. 31, 1968 211 App1.No.: 772,242 [57] ABSTRACT An electrophotographic liquid-developing method comprising controlling the polarity of the toner by varying the mixing pro- [30] Forms 'Apphafion Pnomy Dam portion of the dispersion media and/or the temperature of the Nov. 6, 1967 Japan ..42/7099| developer solution. An electrostatic charge-substrate having I an electrostatically charged latent image is immersed in the 52] 65.0. ..117/37 LE, 117/93.4 A, 252/621 7 developer solution to convert such latent image into a visible s1 1 Int. Cl ..G03g 13/10, 603g 9/04 Said W 501mm comprises a Ionetconsisfing of [58] FieldofSearch....- .,....@117/37 LE,93.4-A;355/10; y P e Particles and at least one resin selected from the v 252/621 group consisting of alkyd resin, phenol-resin and vinyl resin,

and a carrier liquid in which said toner is dispersed. The carri- 56 R f was C-ted er liquid comprises a mixture of two dispersion media having 1 2 er I different affinities to said resin. Dispersion media having a UNlTED STATES PATENTS larger affinity to the resin include halogenated hydrocarbons,

- aromatic hydrocarbons and petroleum hydrocarbons contain- 3,507,679 4/1970 Metcalfe 61'. 81. ..11 7/37 ing aromatic i g i i p i media having a Smaller 3,058,914 10/1962 Metcalfe et a1. ...117/37 X ffi to the resin include iSoparaf-finic and mm 3,220,830 Ill 1965 Kashrwabara... ..1 17/37 X hydrocarbons 3,251,687 5/1966 Fohl et 252/62.1 X 3,296,140 1/ 1967 Zabiak ..252/62.1 14 Claims, 1 Drawing Figure VOLTAGE If THICKNESS METHOD FOR LIQUID-DEVELOPING AN ELECTROSTATIC IMAGE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a novel method for liquid-developing in electrophotography, in which a visible image can be obtained as a negative or a positive selectively on an electrophotographic copying sheet or recording sheet after an electrostatic latent image is formed thereon in a conventional manner. In particular, it relates to a liquid-developing method in electrophotography in which the polarity of a toner having certain ingredients is adapted to be controlled by varying either the mixing proportion of the dispersion media constituting the carrier liquid, or the temperature of said carrier liquid.

The term electrostatic image which may appear in the following description is defined as an electrostatically charged latent image on an electrostatic charge-substrate like an electrophotographic copying sheet or an electrostatic recording sheet, which may be convertible to a visible image by proper development. 7

2. Description of the Prior Art Liquid-developing methods known in the art are the socalled positive-to-positive developing method in which a charged latent image on a copying sheet or a recording sheet is developed in a developer containing a dispersed toner which is charged in the opposite polarity to the latent image, and the so-called negative-to-positive developing method in which an electrostatically negatively charged latent image on a copying sheet or a recording sheet is developed in a developer solution in which is dispersed a toner having the same polarity with the latent image area. The developer solution used in the aforesaid methods normally comprises a condensed toner which is a mixture of pigments, a polarity-control agent (asphalt, rosin or synthetic resin are generally used) which gives a positive or negative charge to the pigment particles used and a small amount of a solvent, and a dispersion medium (which constitutes the carrier liquid) of high electric resistance and low inductance ratio, in which said toner is dispersed. The toner is required to have a charge of distinct polarity in the carrier liquid and sufficient electric potential for adhering by electrophoresis, to the electrostatic latent image area on the copying sheet. In practice, however, a combination of pigment, polarity-control agent and the carrier liquid that will meet with the aforementioned characteristic is still being sought through trial and error, though some specific combinations have been disclosed in the prior art. Only a limited number of specific combinations of certain kinds of condensed toners and the carrier liquid therefor have been put on the market their use has been specified for either positiveto-positive development or negative-to-positive development. Furthermore, the developer solutions must be made in at least two different kinds depending on whether the electric potential in the electrostatic latent image area of the copying sheets is negative or positive.

SUMMARY OF THE INVENTION Unlike the developing methods hereinabove described, in which a positive image or a negative image is formed in a specific combination of copying sheets or recording sheets and the developer solution, the primary objective of the present invention is to provide a unique liquid-developing method for converting an electrostatic latent image on a sheet into a visible image as a positive or a negative selectively by means of controlling the electric charge of the toner to be positive or negative by varying the mixing ratio of the dispersion media constituting the carrier liquid in which a special toner is dispersed, or by changing the temperature of said carrier liquid.

in other words, in a developer solution according to this invention there is used a condensed toner in which at least one kind of alkyd resin, phenol resin and vinyl resin is applied to the pigment particles for controlling the polarity thereof, and

the carrier liquid which is a mixture of dispersion media having a peculiar affinity to the aforementioned resins, so that the electric charge of the toner can be desirably controlled by varying the mixing ratio of the dispersion media or the temperature of the carrier liquid. Furthermore, the electric charge of the toner can be varied in either way even if the carrier liquid contains only one dispersion medium by changing the temperature of the carrier liquid. Now, the present invention will be described in further detail with reference to the accompanying drawing.

Curve 1 in the FIGURE indicates the relationship between the thickness of the adsorption layer and the electric potential (M) of resins in general, while curve 2 shows the same relationship for special resins that will create variations depending upon the kind of polarity-controlagents used. Our experiments proved thatthe toner in which the carbon black is coated with the alkyd resins shows changes as shown in curve 2 and that the toner in which carbon black is coated with asphalt or rosin varies like curve 1. These facts indicated an adjustability of the thickness of the adsorption layer corresponding to said curve 2 by varying the dispersion media or temperature. It was thus discovered that a suitable mixture of (l) a dispersion medium having greater affinity and (2) a dispersion medium having smaller affinity to the absorption layer consisting of alkyd resin, or that variations in the temperature of such mixture or the carrier liquid, will change the thickness of the alkyd resin layer adhered to the carbon black,

whereby the electric charge of the toner is variable either from negative to positive or vice versa. It was further discovered that these facts hold true also with phenol resin and vinyl resin.

Some of possible dispersion media having a large affinity to the alkyd resin, phenol resin or vinyl resin are partially or entirely halogenated hydrocarbons such as C C1 (C CI F) CI-IC1F CCl F-CC1F or aromatic hydrocarbons such as toluene, benzene, petroleum hydrocarbon including aromatic ingredients, for example, Naphtha No. 6, Solvesso 100, Solvesso 150 (all are products of Esso Standard Oil Co.) and ligroin. The dispersion media having smaller affinity to the aforesaid resins include, for example, such isoparaffinic hydrocarbons as lsopar G, lsopar H (products of Esso Standard Oil Co.), Super-VM&P Naphtha (product of Shell Oil Co.) and paraffinic hydrocarbon such as normal paraffin like n-hexane. The halogenated hydrocarbon include two types; namely chlorofluoro-hydrocarbon such as Daiflon S-l (CCl F), Daiflon S-3 (CCl F-CClF Daiflon S-2 (CCl F) and chlorinated hydrocarbon (CC 1 Ligroin is refined solvent naphtha having a density of 0.850 to 0.870 and a distillation range at 760 mm.; percentage recovered at C. not more than 5; percentage recovered at C. not less than 90; end point= not above 155 C.

lsopar G is a petroleum hydrocarbon containing 99 volume percent of isoparaffinic hydrocarbon.

lsopar H is a petroleum hydrocarbon containing 99 volume percent of isoparafiinic hydrocarbon.

Solvesso 100 is a petroleum hydrocarbon containing 98 volume percent of aromatic hydrocarbon.

Solvesso is a petroleum hydrocarbon containing 97.3

volume percent of aromatic hydrocarbon.

Naphtha No. 6 is a petroleum hydrocarbon containing 25 volume percent of aromatic hydrocarbon and 70 volume percent of paraffinic hydrocarbon.

Super Naphtha is a petroleum hydrocarbon containing 15 volume percent of aromatic hydrocarbon and 80 volume percent of paraffinic hydrocarbon.

However, the degree of affinity may be varied even in the aforementioned groups of dispersion media having greater or smaller affinities. For example, the polarity control of the toner is possible by a combination of Daiflon S-2 and Daiflon 5-3 in the group of chlorofluoro-hydrocarbons and by subsequent variation of their composition ratio or temperature. Therefore, in the present invention, the degree of affinity is referred to only in a relative sense.

TABLE I The limit The limit percentage of percentage of dispersion dispersion medium A at medium A at which toner which toncr Dis ersion is negatively is positively Dispersion medium A me ium B charged charged 1. Daiflon Si (CCIQF) Daiflon S2 80% or morc.. 70% or less.

(001210 2. Isopar G (isoparatfinic hydrocar- .....clo 70% or more. 60% or less.

on 3.tl)lsor)iar H (isopnratiinic hydrocardo do Do.

on 4. Ligroin (petroleum hydrocarbon do do D0.

containing aromatic ingredients). 5. Solvesso-1 o (petroleum hydrodo 60% or more"-.. 50% or less.

geirbpn) containing aromatic ingreen s 6. Naphtha No. 6 (petroleum hydro- -....do 30% or more. ..20% or less.

pfirbpr; containing aromatic ingreen s 7. Toluene (aromatic hydrocarbon) do 60% or more. 60% or less. 8. Super naphtha (petroleum hydro- .do 40% or more..-" 30% or less.

cerbttn; containing aromatic ingren s 9. Perchloroethylene (chlorinated hydo 60% or more 50% or less.

drocarbon) The alkyd resins which may be used in the process of the present invention include Super Becksol J-l 350, 1-1351 and J- 571 which are long oil alkyd resins modified with soya-bcan oil, Super Becksol 1-537 which is a long oil alkyd resin modified with sunflower oil (the products of Dainippon Ink and Chemical Incorporated). Among the phenol resins are Nikanol HP-lOO (manufactured by Japan Gas-Chemical Co., Inc.), Tamanol 520 (manufactured by Arakawa Forest Chemical Industries Ltd. Japan), PP-8l0 (Gun-ei Chemical Industry Co., Ltd. Japan), Super Becasite I00 (manufactured by Dainippon Ink and Chemical Incorporated), and as the vinyl resins, polymers or copolymers obtained from acrylic acids, methacrylic acids and other vinyl monomers, such, for example, as laurylmethacrylate-dimethyl or diethyl aminoethylmethacrylate resins, and laurylmethacrylate styrene resins, are used.

The pigment particles which may be used in the process of this invention include such well-known pigments as carbon black, aniline black and spirit black.

As described above, it is the object of the present invention to provide a method for developing a positive or negative electrostatic latent image on a copying sheet or a recording sheet into a desired corresponding visible image, which may be either positive or negative, using a developer solution prepared by dispersing the aforesaid concentrated toner into a carrier liquid consisting at least one dispersion medium having a different affinity to alkyd resin, said method comprising controlling the charge of said toner by varying the mixing proportion of said dispersion media or by changing the temperature of said carrier liquid. Thus, the method of this invention has an advantage that either a positive or negative image as desired may be formed on the copying paper or recording paper from the same original if such concentrated toner and at least one of the dispersion media are prepared.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE shows the relationship between the thickness of the absorption layer (consisting of a part of a resin as a polarity-control agent and two kinds of dispersion media) with which pigment particles are covered and the electric potential (g) of toner consisting of the resin and pigment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1 A concentrated toner was prepared by adding to grams of the pigment particles (Mogul A, carbon black manufac- I tured by Cabot of the USA.) 20 grams of alkyd resin (a long oil alkyd resin manufactured by Dainippon Inc. and Chemical Incorporated under trade name of Super Becksol Jl35l and grams of toluene and ball-milling the mixture for more than 10 hours. When 1 gram of the concentrated toner thus obtained was dispersed in approximately 100 ml. of the carrier liquid consisting of the respective mixed dispersion media indicated in Table 1 below, it was possible freely to control the charge of the toner either to the positive or negative sign by varying the proportion of said dispersion media. The limit percentages (vol. of the dispersion medium A in the mixed dispersion media at which the toner changes from one sign to wea he .erss qwnirieh From Table 1 given above, it is recognized that, although it is generally believed that a toner comprising alkyd resin adsorbed in the pigment particles is negatively charged, it may take a negative charge when a dispersion medium which has a lower, affinity to the alkyd resin is used and it may be positively charged when a dispersion medium having a higher affinity to the alkyd resin is employed. Thus, even a toner composed of the pigment and alkyd resin may be positively charged to a sufiicient degree when such toner is dispersed in simple Daiflon S (chlorofluoro-hydrocarbon EXAMPLE 2 Three types of electrophotographic developer solutions were prepared by dispersing approximately 1 gram of the concentrated toner prepared according to Example 1 in 100 ml. respectively of the following carrier compositions:

a. Carrier liquid consisting of a mixture of dispersion media composed of equal parts of Daiflon S (CCl F-Ccl F) and Daiflon S (CCl F) b. Carrier liquid consisting of a mixture of dispersion media composed of one part of Daiflon S and 2.33 parts of Daiflon S solution (c) the sign of the charge did not change to positive even when the solution was heated to 40 C.

EXAMPLE 3 A concentrated toner was prepared by mixing 5 grams of phenol resin (manufactured by Japan Gas-Chemical Co., inc. and commercially available under the trade name Nikanol HP-lOO") and 50 grams of toluene with 5 grams of the pigment particles (United HAF," carbon black, manufactured by United Carbon of USA.) and ball-milling the mixture thus obtained for over hours. When 1.2 grams of the prepared concentrated toner was dispersed in 100 ml. of the mixed dispersion media comprising Solvesso 100 (petroleum hydrocarbon containing aromatic ingredients) and lsopar H (isoparaffinic hydrocarbon) at the proportion by volume of 60 percent or more to 40 percent or less, the charge of the toner was negative, and when the said mixing proportion by volume was 50 percent or less to 50 percent or more, the charge was positive, thus the control of the charge sign being effectively conducted. Nikanol HP-lOO is an alkyl phenol modified xylene resin which is a light yellow solid, having a color value of less than 8 and a viscosity (cp.) of 200-400.

EXAMPLE 4 Percentages of Solvesso 100 to the total volume (percent) Percentage at Percentage at Quantity of phenol which toner is which toner is resin (wt. percent to negatively positively pigment particles) charged. charged.

200 40% or more 35% or less. 300 30% ormore 25%orless. 400 20% or more or less.

it is evident from the table that a'variario'nmiiz anm of phenol resin involves a change in the composition proportion of the toner, but, in any case, it is possible to control the charge of the toner so that it will be either positive or negative.

EXAMPLE 5' A concentrated toner was prepared by mixing 5 grams of the pigment particles (Mitsubishi No. 44," carbon black manufactured by Mitsubishi Kasei) with 10 grams of 50 percent toluene solution of lauryl methacrylate dimethylaminoethylmethacrylate resin (at the polymerization molar ration of 90 to 10), 1 gram of manganese naphthionate (containing 10 percent Mn) and 34 grams of lsopar H and ball-milling the mixture thus formed. 0.5 gram of concentrated toner was then dispersed in 100 ml. of lsopar H, thereby obtaining a developer solution. This developer showed a positive charge at normal temperature but the charge was negative when the solution was heated to 60 C. and thereafter suddenly cooled down to 10 C.

What is claimed is:

l. in a method for liquid developing an electrostatic latent image to form a visible image by immersion in a liquid developer comprising a dispersion of an electrically charged toner in a carrier liquid, said toner comprising fine particles of carbon black coated with alkyl resin with a weight ratio of alkyl resin to carbon black of 4/ l said carrier liquid consisting essentially of a mixture of (a) a first dispersion medium of (CCl F) having a relatively large solubility to said resin, and (b) a second dispersion medium having a relatively small solubility to said resin and selected from the group consisting of l CCl F; (2) perchloroethylene; (3) petroleum hydrocarbon containing about 99 volume percent of isoparaffinic hydrocarbon; (4) ligroin; (5) petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon; (6) petroleum Vol. of (b) to Vol. of (b) to give negatively give positively (b) Component charged toner charged toner (l) or more 70% or less. (2). 60% or more..." 50% or less. (3) 7 60% or less. (4) Do. (5). 50% or less. (6)-... 30%orrnore... 20%orless. (7) 40% or more 30% or less. (8) 60% or more... 50% or less.

2. The method of claim 1 wherein (b) is CCl F.

3. The method of claim 1 wherein (b) is perchloroethylene.

4. The method of claim 1 wherein (b) is petroleum hydrocarbon containing about 99 volume percent of isoparaffinic hydrocarbon.

5. The method of claim 1 wherein (b) is ligroin.

6. The method of claim 1 wherein (b) is petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon.

7. The method of claim 1 wherein (b) is petroleum hydrocarbon containing about 25 percent of aromatic hydrocarbon and 70 volume percent of paraffinic hydrocarbon.

8. The method of claim 1 wherein (b) is petroleum hydrocarbon containing 15 volume percent of aromatic hydrocarbon and 80 volume percent of paraffinic hydrocarbon.

9. The method of claim 1 wherein (b) is toluene.

10. in a method for liquid developing anelectrostatic latent image to form a visible image by immersion in a liquid developer comprising a dispersion of an electrically charged toner in a carrier liquid, said toner comprising fine particles of carbon black coated with phenol resin, said carrier liquid consisting essentially of a mixture of (a) a first dispersion medium of petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon and having a relatively large solubility to said resin, and (b) a second dispersion medium of petroleum hydrocarbon containing about 99 volume percent of isoparaffinic hydrocarbon and having a relatively small solubility to said resin, the improvement comprising adding to and mixing with said liquid developer having a first electrical polarity an additional quantity of one of said dispersion mediums (a) or (b) in an amount so that the resultant composition has a volume concentration of the (b) component within the range of opposite polarity, for the various weight ratios of phenol resin to carbon black, as defined by the following table:

Weight ratio of V01. of (b) to V01. of (b) to phenol resin to cargive negatively give positively bon black charged toner charged toner 1/1 60% or more. 50% or less.

t 40% or more 35% or less. 30% or more..." 25% or less. 4/1 20% or more 15% or less.

14. The method of claim 10 wherein the weight ratio of resin to carbon black is 4/1. 

2. The method of claim 1 wherein (b) is CCl3F.
 3. The method of claim 1 wherein (b) is perchloroethylene.
 4. The method of claim 1 wherein (b) is petroleum hydrocarbOn containing about 99 volume percent of isoparaffinic hydrocarbon.
 5. The method of claim 1 wherein (b) is ligroin.
 6. The method of claim 1 wherein (b) is petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon.
 7. The method of claim 1 wherein (b) is petroleum hydrocarbon containing about 25 percent of aromatic hydrocarbon and 70 volume percent of paraffinic hydrocarbon.
 8. The method of claim 1 wherein (b) is petroleum hydrocarbon containing 15 volume percent of aromatic hydrocarbon and 80 volume percent of paraffinic hydrocarbon.
 9. The method of claim 1 wherein (b) is toluene.
 10. In a method for liquid developing an electrostatic latent image to form a visible image by immersion in a liquid developer comprising a dispersion of an electrically charged toner in a carrier liquid, said toner comprising fine particles of carbon black coated with phenol resin, said carrier liquid consisting essentially of a mixture of (a) a first dispersion medium of petroleum hydrocarbon containing about 98 volume percent of aromatic hydrocarbon and having a relatively large solubility to said resin, and (b) a second dispersion medium of petroleum hydrocarbon containing about 99 volume percent of isoparaffinic hydrocarbon and having a relatively small solubility to said resin, the improvement comprising adding to and mixing with said liquid developer having a first electrical polarity an additional quantity of one of said dispersion mediums (a) or (b) in an amount so that the resultant composition has a volume concentration of the (b) component within the range of opposite polarity, for the various weight ratios of phenol resin to carbon black, as defined by the following table:
 11. The method of claim 10 wherein the weight ratio of resin to carbon black is 1/1.
 12. The method of claim 10 wherein the weight ratio of resin to carbon black is 2/1.
 13. The method of claim 10 wherein the weight ratio of resin to carbon black is 3/1.
 14. The method of claim 10 wherein the weight ratio of resin to carbon black is 4/1. 